AMOSSG/4-SN No. 2

26/6/03

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

FOURTH MEETING

Montreal, 15 to 18 September 2003

Agenda Item	5:	Aerodrome observation requirements

OVERVIEW OF PAST AND EXPECTED PROGRESS WITH RESPECT TO AERODROME OBSERVATION REQUIREMENTS

(Presented by the Secretary)

SUMMARY
A brief summary of the progress made by the group is given with respect to aerodrome observation requirements together with an overview of outstanding tasks for consideration by the group.

1.	INTRODUCTION

1.1	This paper summarizes the tasks that are to be addressed by the group that concern aerodrome observation requirements together with an indication of previous discussions and in some cases suggested courses of action.

1.2	The primary sources of the tasks that the group is expected to consider are from the previous meetings of this group (ongoing tasks), the MET Divisional Meeting (2002) (new tasks) and the forty-fourth Meeting of the European Air Navigation Planning Group (EANPG) (new tasks).

2.	DISCUSSION

2.1	Amendment 73 to Annex 3 — Meteorological Service for International Air Navigation

2.1.1	The group will recall that much of its work over the previous two meetings concerned the preparation of an update to Chapter 4 of Annex 3 which was to be submitted to the MET Divisional Meeting (2002) as a part of the proposed Amendment 73 to Annex 3. This was carried out in two parts:

a)	draft provisions related to the introduction of prevailing visibility (some States were concerned about the concept; therefore, as a separate item it could have been easily excluded from the Amendment if deemed to be necessary), and

b)	draft provisions related to the rest of Chapter 4 of Annex 3.

2.1.2	The group will be pleased to note that MET Divisional Meeting (2002) in its Recommendation 2/1 endorsed the proposals made by the group for amendments to Annex 3 including the introduction of the concept of prevailing visibility. However, two modifications were made to the original proposal from the group. Firstly, it was considered to be premature for an enabling clause to be placed in Annex 3 for the dissemination of METAR, SPECI and TAF in the BUFR code form; this will be discussed in more detail in Section 2.5 below. Secondly, the proposed change of the definition of "vicinity" was not accepted by the meeting; this will be discussed in more detail in Section 2.3 below.

2.2	Harmonization of SPECI criteria with TAF change criteria

2.2.1	The MET Divisional Meeting (2002) in its Recommendation 2/3 b) invited ICAO, in consultation with the World Meteorological Organization (WMO) to consider the need for harmonizing the criteria for issuance of SPECI and those for including change groups in TAF.

2.2.2	The criteria for issuance of SPECI are defined in Annex 3, paragraph 4.3.4. It should be borne in mind that sub-paragraph d) specifies that certain thresholds for changes in the wind should be established by the meteorological authority in consultation with the appropriate ATS authority and operators concerned. Amendment 73 to Annex 3, should it be adopted by the ICAO Council, will make one change in that all references to "visibility" will be replaced by "prevailing visibility".

2.2.3	The criteria for including change groups in TAF are defined in Annex 3, paragraph 6.2.5. It should be borne in mind that sub-paragraph h) specifies that additional change criteria can be based on local aerodrome operating minima, as agreed between the meteorological authority and the operators. There are no changes to this paragraph in the proposed Amendment 73 to Annex 3.

2.2.4	The group may wish to agree that there is an operational need to harmonize these two sets of criteria and to address any difficulties that this might present and how they might be overcome. Furthermore, the group may wish to agree that the Secretary should develop a draft amendment to Annex 3 in time for the AMOSSG/5 Meeting.

2.3	The use of, and definition of the term "vicinity"

2.3.1	The group will recall that it was proposed that the term "vicinity" should effectively be deemed to represent all points which lie between 8 km and 16 km from the aerodrome reference point.

2.3.2	At the MET Divisional Meeting (2002) there was some concern expressed regarding the change to the definition of the term "vicinity", which was proposed to be redefined in terms of the aerodrome reference point, in that the reference point of an aerodrome did not necessarily represent a suitable location for such a definition at all aerodromes. It was considered that at some aerodromes the reference point was not situated at a central location within the perimeter of the aerodrome and consequently it was possible that areas 8 km from this point were still considered to be "at the aerodrome". Consequently, further consideration of this definition was referred back to ICAO by the MET Divisional Meeting (2002), (Recommendation 2/3 e) refers). The Air Navigation Commission, when taking action on this recommendation, requested that the group develop proposals in time for Amendment 74 to Annex 3.

2.3.3	The group may wish to consider the definition of the term "vicinity" in the light of the comments made by the MET Divisional Meeting (2002). Furthermore, the group may wish to agree that the Secretary should prepare a draft amendment to Annex 3 in time for the AMOSSG/5 Meeting taking into account the views expressed by the group.

2.4	The attainable accuracy of observation or measurement

2.4.1	The Air Navigation Commission (ANC) at ninth Meeting of its 153rd Session instructed the Secretariat to invite WMO to update the attainable accuracy of observation or measurement as given in Attachment B to Annex 3.

2.4.2	It is expected that a report on the progress made to this end will be presented by WMO with a view to including any updates to Attachment B to Annex 3 as a part of Amendment 74 to Annex 3.

2.5	Migration plans for the use of table-driven code forms

2.5.1	The MET Divisional Meeting (2002), in its Recommendation 2/5 invited WMO to develop a migration plan concerning the use of table-driven code forms for the dissemination of METAR/SPECI and TAF.

2.5.2	The group may wish to note that the WMO Congress has endorsed the timetable developed by the relevant Commission for Basic Systems (CBS) expert team. This timescale will introduce such codes in two phases. Firstly, that table-driven codes could be used, by those States that wish to do so, in parallel with the traditional alphanumeric codes from 2007 and that the table-driven codes would become fully operational from 2015. The first stage of this plan will necessitate the development of enabling provisions in Annex 3 as a part of Amendment 74. The group may wish to agree that such draft provisions should be developed by the Secretary in time for the AMOSSG/5 Meeting.

2.5.3	The group may also wish to note that an ICAO/WMO ad-hoc group addressed, in May 2003, several technical issues related to the migration. That group was assisted by experts in the operation of the aeronautical fixed telecommunication network (AFTN).

2.5.4	Firstly, the introduction of table-driven codes could cause difficulties in some AFTN switching centres, assuming that there will be a period of overlap resulting in the dissemination of such information in parallel with the alphanumeric code forms as some switching centres would not have the capacity to deal with the potential for additional data volumes. Furthermore, AFTN circuits are not able to carry digital codes which implies that the introduction of the BUFR code form needs to be coordinated with the introduction of circuits on which digital data can be disseminated. These circuits will have to be introduced on a regional basis and ultimately between regions.

2.5.5	Secondly, it was suggested at the MET Divisional Meeting (2002) that the character form for the representation and exchange of data (CREX) code form could be used during the transition to table- driven codes. Potentially, this would have alleviated the problems concerning the use of digital codes on the AFTN. However, it should be noted that the AFTN would also not be able to accommodate the CREX code form owing to the likely length of messages that would be required using this code. Therefore, the ad-hoc group ruled out the potential use of the CREX code form during any migration plan.

2.6	Revision of present weather and recent weather requirements

2.6.1	The group will recall that at the AMOSSG/4 Meeting it was concluded that no changes to the requirements for present weather or recent weather were necessary at that time. However, the group agreed that this review should remain on the work programme of the group for further consideration.

2.6.2	The requirement to re-address this task was emphasized by the MET Divisional Meeting (2002) which, in its Recommendation 2/3 d) invited ICAO, in consultation with WMO to re-evaluate the requirements for present weather and recent weather taking into account the capacity of automatic systems.

2.6.3	It is expected that the members of the group will prepare study notes concerning specific proposals for any changes to the requirements in this area bearing in mind the main operational purpose of aerodrome observations i.e. for flight planning purposes and not as basic meteorological observations. The group may wish to discuss the proposals in light of the recommendation of the MET Divisional Meeting (2002).

2.7	The use of fully automatic observations during operational hours

2.7.1	The MET Divisional Meeting (2002) in its Recommendation 2/3 c) invited ICAO, in consultation with WMO to study the expansion of the use of fully automatic observing systems to include operational hours including the new concept of "required level of meteorological services".

2.7.2	Clearly the requirements here relate to Agenda item 6 of this meeting in that the capabilities of automatic observing systems need to be assessed. It should be stressed, however, that the requirements for information should not be affected by the capability to fulfill them. It is the requirements that should drive the development of technology although, clearly these developments need to be borne in mind when considering the relative needs for individual pieces of information. Consequently, the group may wish to return to this issue when considering Agenda item 6.

2.7.3	Two sets of criteria exist in the possible discrimination of international aerodromes which the group may wish to consider for any proposals regarding the use of fully automatic observing systems during operational hours.

2.7.4	Firstly, the definitions of aerodromes with runways designated under the various categories given below for which there are already many examples of separate provisions given in a number of ICAO Annexes:

Non-instrument runway. A runway intended for the operation of aircraft using visual approach procedures.

Instrument runway. One of the following types of runways intended for the operation of aircraft using instrument approach procedures:

a)	Non-precision approach runway. An instrument runway served by visual aids and a non-visual aid providing at least directional guidance adequate for a straight-in approach.

b)	Precision approach runway, category I. An instrument runway served by ILS and/or MLS and visual aids intended for operations with a decision height now lower than 60 m (200 ft) and either a visibility not less than 800 m or a runway visual range not less than 550 m.

c)	Precision approach runway, category II. An instrument runway served by ILS and/or MLS and visual aids intended for operations with a decision height lower than 60 m (200 ft) but not lower than 30 m (100 ft) and a runway visual range not less than 350 m.

d)	Precision approach runway, category III. An instrument runway served by ILS and/or MLS to and along the surface of the runway and:

A -	intended for operations with a decision height lower than 30 m (100 ft), or no
decision height and a runway visual range not less than 200 m.

B -	intended for operations with a decision height lower than 15 m (50 ft), or no decision	height and a runway visual range less than 200 m but not less than 50 m.

C -	intended for operations with no decision height and no runway visual range
limitations.

2.7.5	Secondly, there are five categories or aerodromes available for each of the Regional Plans which are allocated to all international aerodromes (given below):

a)	RS - international scheduled air transport, regular use;

b)	RNS - international non-scheduled air transport, regular use;

c)	RG - international general aviation, regular use;

d)	AS - international scheduled air transport, alternate use, and

e)	ANS - international non-scheduled air transport, alternate use.

2.7.6	The group may wish to note that the categories listed in 2.7.5 are simply used to inform users of the usage of the various aerodromes in States and no implications are made regarding the technical capabilities that may exist at any particular aerodrome. The Secretariat view is that the use of such criteria would not be appropriate for the purpose of creating proposals for the operational use of automatic observation systems. Therefore, the group may wish to agree that the criteria listed in 2.7.4 should be used in some manner to identify those situations in which fully automatic observations can be used during operational hours bearing in mind that the criteria given in 2.7.4 already relate to the meteorological conditions at the aerodrome.

2.7.7	It is expected that members of the group will report on issues that may affect the use of fully automatic observing systems during operational hours and provide criteria or proposals describing circumstances that may make it appropriate to use such systems. Discussion is expected to identify avenues for further study that may be required in order to accommodate the use of such systems during operational hours so that the Secretary would be able to prepare a draft amendment to Annex 3 in time for the AMOSSG/5 Meeting.

2.8	The use of modern observing techniques including remote sensing

2.8.1	The group will recall that it was agreed at the AMOSSG/3 Meeting that a progress report would be provided by Michel (France) on the use of remote sensing techniques for the purpose of improving the generation of automatic aerodrome observations.

2.8.2	It is expected that such a report will be given by Michel and any other reports from members of the group would be welcomed regarding modern observing techniques. The group may wish to agree that initially these issues should be addressed in guidance material to be introduced in the proposed manual on the use of automatic observing systems.

2.9	The use of the term "CAVOK"

2.9.1	The MET Divisional Meeting (2002) in its Recommendation 2/3 a) invited ICAO, in consultation with WMO to re-evaluate the appropriateness of the use of the term "CAVOK" in meteorological reports and aerodrome forecasts taking into account the requirements of ATS units and users as well as the potential costs of any proposed changes. This was as a result of suggestions that by using the term "CAVOK" the requirements of some users and States were not being met as cloud information was required up to 7 600 m (25 000 ft).

2.9.2	The group may wish to note that the Commission felt that the term "CAVOK" had been in use for many years with no known incidents. Furthermore the Commission agreed that the high costs involved for many States cast doubt on the validity of pursuing the matter any further. As a consequence the Commission agreed that work on this issue should not be pursued by this group any further.

2.10	Update and presentation of cloud base height in ATS units

2.10.1	The EANPG at its forty-fourth meeting, in its Conclusion 44/16 identified the need for provisions in Annex 3 to cater for the update and presentation of cloud base height in air traffic services (ATS) units. The Commission took action on this conclusion by referring the issue to this group for resolution.

2.10.2	Amendment 72 to Annex 3 upgraded paragraph 4.1.8 to a Standard which now requires that surface wind, runway visual range (RVR) and the height of cloud base shall be assessed or measured by an integrated automatic observing system at aerodromes with runways intended for Category II and III instrument approach and landing operations. Provisions already exist in Annex 3 for the display of such information relating to surface wind (Section 4.5) and RVR (Section 4.7) in ATS units whereas no provisions exist for the display of information relating to the height of cloud base.

2.10.3	The group may wish to agree that there is a need to develop provisions in Annex 3 relating to the display of the height of cloud base in ATS units and that the Secretary should develop a draft amendment to Annex 3 in time for the AMOSSG/5 Meeting.

2.11	The calculation of cross wind and tail wind for take-off and landing

2.11.1	The EANPG at its forty-fourth meeting, in its Conclusion 44/17 invited ICAO to study the need for guidance material concerning the calculation of cross wind and tail wind components for take-off and landing operations and in particular in the case where gusts are reported. The Commission expressed the view that the straightforward calculation of these components had been routinely performed for many years (for mean winds) with no apparent difficulties. The Commission therefore referred the issue of guidance material relating to such calculation in the situation where gusts are reported to this group for consideration.

2.11.2	The group may wish to consider whether there is a need for guidance material and/or provisions to cater for the reporting of gusts in the calculation of cross wind and tailwind for take-off and landing operations.

3.	ACTION BY THE GROUP

3.1	The group is invited to;

a)	agree that there is an operational need to harmonize the criteria for issuing SPECI with the criteria for change groups within TAF and that the Secretary should develop a draft amendment to Annex 3 in time for the AMOSSG/5 Meeting;

b)	agree that the definition of "vicinity" should be changed in light of the concerns raised by the MET Divisional Meeting (2002) and that the Secretary should develop a draft amendment to Annex 3 in time for the AMOSSG/5 Meeting taking the views of the group into account;

c)	consider whether any changes should be made to the requirements for the reporting of present weather and/or recent weather;

d)	agree that enabling provisions for the dissemination of METAR/SPECI and TAF in the BUFR code form should be developed and that a draft amendment to Annex 3 should be developed by the Secretary in time for the AMOSSG/5 Meeting;

e)	agree that guidance should be included in the proposed manual on the use of automatic observing systems to accommodate the use of modern observing techniques, e.g. remote sensing;

f)	agree that further studies should be carried out in order to establish a framework for the use of fully automatic observing systems during operational hours based on the runway categories and based on those studies, to task the Secretary to develop a draft amendment to Annex 3 to accommodate the use of fully automatic observing systems during operational hours in time for the AMOSSG/5 Meeting;

g)	agree that the Secretary should develop a draft amendment to Annex 3 for the display of the height of cloud base in ATS units in time for the AMOSSG/5 Meeting, and

h)	consider whether there is a need for guidance material and/or provisions concerning the calculation of cross wind and tail wind for take-off and landing operations.

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